David Plant, provides an excellent presentation of Kepler, the astrologer, including his background.For example...

“Johannes Kepler was born on 6th January 1572 (NS) at Weil-der-Stadt in the German province of Swabia.His grandfather had been mayor of the town but the Kepler family fortunes were in decline.His father was a bullying adventurer who earned a precarious living as a mercenary soldier and deserted the family when Johannes was 17.His mother, an inn-keeper’s daughter, had a reputation for witchcraft.Born prematurely, Johannes was weak and sickly.He spent a solitary, unhappy childhood, but at least he was fortunate in that the ruling Dukes of Württemburg had created a relatively enlightened system of education in Swabia.With a view to recruiting the brightest minds for the Protestant clergy, a system of grants and scholarships was available to promising (male) children of poor families, and despite his ill health, Johannes was precociously brilliant.”

Where Johannes was to go from there was anyone’s guess, but it is noteworty that he had to contend with the rather warped view of the cosmos of his 16th Century day.I.e....

One authority noted that starting around 600 B.C.E., “a number of early philosophers in the Ionian city of Miletus began the break from traditional beliefs with the first attempts to formulate rational cosmologies based on empirical observations -- as limited as these observations were.Philosophers such as Thales, Anaximander, and Anaximenes produced a few related theories generally describing a geocentric universe [geo = earth at the center], with a flat disc Earth floating on an infinite cosmic ocean, capped by air, and surrounded by the circling Sun, Moon, and planets, all within a celestial sphere of stars.”

“A late contemporary of the Milesians, Pythagorus built upon their geocentric concepts in his cosmology that was the first to be centered upon a spherical Earth, and surrounded by celestial bodies which moved in perfect circular motions, each of which was borne by a progression of separate spheres, with the outermost sphere being the sphere of stars.The compound motion of these spheres as they rotated around the immobile Earth was said by the Pythagoreans to produce a celestial music through their perfect harmony. The fundamental Pythagorean idea of perfectly ‘uniform circular motions’ would be unquestioned in western cosmology for nearly two thousand years.”

At least until the time of Kepler, who saw ellipses instead of circles.Heresy!

“This basic Pythagorean structure of the cosmos was later formalized sans music and mysticism in a vastly more complex mathematical model by Eudoxus of Cnidos (390 - 340 BCE). Using 27 ‘homocentric spheres,’ he was able to describe the observed motions of the celestial bodies, albeit imperfectly.The philosophers who followed would build upon his astronomic model by adding ever greater numbers of spheres to reduce the degree of observed error, reaching a total of 56 as revised by Aristotle (384-322 BCE).Aristotle was also the first to interpret the Eudoxian system as a description of reality rather than as just a mathematical model of the celestial sphere.”

Johannes Kepler in his Hamonicies mundi of 1619, returned to the music connection, in an “almost Pythagorean eulogy to the mathematical harmonies that exist within the celestial sphere, and which contains his third law of planetary motion.”